Production of tungsten halogen lamps

ABSTRACT

A method of making a tungsten halogen incandescent lamp in which iodine is introduced into the lamp envelope in the form of an iodide or hydroiodide of an element of Group IV of the Periodic Table which is an involatile solid at room temperature.

United States Patent 9 1 Coxon et al.

PRODUCTION OF TUNGSTEN HALOGEN LAMPS Inventors: George Eric Coxon; John Michael Rees, both of London, England Assignee: Thorn Electrical Industries Limited,

London, England Filed: Aug. 10, 1971 App1. No.: 170,627

Foreign Application Priority Data 11 3,738,729 June 12, 1973 [56] References Cited UNITED STATES PATENTS 3,091,718 5/1963 Shurgan 313/222 FOREIGN PATENTS OR APPLICATIONS 763,062 7/1967 Canada 313/223 900,200 7/1962 Great Britain 313/223 Primary Examiner-Charles W. Lanham Assistant Examiner-J. W. Davie Attorney-Joseph C. Ryan [57] ABSTRACT 4 Claims, No Drawings lamps of short life. For lamps with an intended life of 1,000 hours or above iodine is necessary, or an iodine compound or a mixture with other halogens with iodine predominating.

There are serious difficulties attendant upon the introduction of elementary iodine into the lamp. Iodine has a vapor pressure which is too high for the lamp to be pumped after introduction of the element, but too low for the iodine to be flushed in at room temperature with the fill gas, such as argon. Cumbersome and expensive techniques are employed to overcome this difficulty, but often involve an undesirable number of manual operations, the risk of introducing harmful impurities or an inability to achieve an accurately controlled dosage of iodine. They also tend to be wasteful of iodine In accordance with this invention iodine is introducedinto a lamp envelope in the form of an involatile solid iodide or hydroiodide of an element of Group IV (IVB) of the Periodic Table, more especially of carbon, silicon or germanium. By solid is meant that the compound is a solid at room temperature. Preferred examples of such solids are iodoform, carbon tetraiodide, silicon tetraiodide and the germanium tetraiodide.

The iodine compounds employed in accordance with this invention are soluble in volatile, non-polar, organic liquids, for example petroleum ether, benzene and toluene, and are preferably dispensed into the lamp in solution and the solvent removed to leave the involatile solid compound in the envelope.

The iodine compound in solution can be accurately dispensed into the envelope and the solvent can be removed by evacuation or by flushing with a dry nonreactive gas. After this the lamp can be evacuated on an exhaust system, which can be a rotary machine commonly used in the manufacture of incandescent lamps, and filled with inert gas to the required pressure. The iodine compound is only dissociated when the lamp is heated, which is usually achieved by light-ing the filament. The preferred procedure is to increase the filament voltage slowly from zero to full voltage over about to 30 seconds to allow the compound to disperse, or to step age" the filament by running at various intermediate voltages, from zero to the rated voltage.

By use of the invention a controlled and accurately repeatable dose can be dispensed into each lamp. After the solvent has been removed, the remaining solid is involatile at room temperature and the lamp can be exhausted and gas-filled on a simple vacuum, gasfilling system of the type used for non-halogen lamps, without the need for cold traps or other devices for protecting rotary pumps, valve plates and other components of the system. Because all the iodine remains as an involatile solid during processing, no special maintenance or safety precautions are required on the exhaust and gasfilling system, and the method is very suitable for high speed production techniques.

The involatile solid compounds defined above have the advantage over gaseous iodine compounds, such as CH I, 011 1 and HI, because the ratio of hydrogen to iodine is lower with CHI and is zero with the compounds used in accordance with the invention. This avoids the difficulty of a reduction in activity of the tungsten transport cycle in the presence of hydrogen (which is useful with bromine or chlorine as halogens, but a disadvantage with iodine).

The following is one example of the practice of this invention:

Iodoform (CI-Il which has a vapor pressure of only 1.7 X 10 torr 23C, is dissolved in toluene to a concentration of 3 percent weight/volume (i.e. 3g CHI in 100 ml. toluene). To maintain a satisfactory tungsten transport cycle in a 240V 500W coiled coil linear lamp, having an efficacy of 20 lm/W and 2,000 hr life, 0.025 ml. of this solution is required. It is introduced by in- V serting the needle of a suitably calibrated syringe into the exhaust tube of a lamp envelope, and injecting the required quantity into the lamp envelope. The solvent is then removed by inserting a hollow needle connected to a dry nitrogen supply, and flushing gas into the lamp until the solvent is removed. Raising the bulb wall temperature to approximately C speeds up this operation.

After this the lamp is processed as a conventional incandescent lamp on a suitable exhaust/gasfilling system, with the bulb at room temperature. After being filled with gas, the lamp is then lit to dissociate and disperse the iodine compound.

We claim:

1. In a method of making a tungsten halogen incandescent lamp having an envelope into which iodine is introduced, said envelope being subsequently evacuated and filled with inert gas, the improvement which comprises introducing said iodine into said envelope in the form of an iodine compound selected from the group consisting of iodides and hydroiodides of elements of Group IV of the Periodic Table, said iodine compound being an involatile solid at room temperature.

2. A method according to claim 1 which includes the steps of introducing said iodine compound into said envelope in solution in a volatile non-polar organic liquid, and thereafter removing said liquid from said envelope thereby to leave said solid iodine compound in said envelope.

3. A method according to claim 1 wherein said iodine compound is selected from the group consisting of CHIg, C14, G614 Ol' 8H4.

4. A method according to claim 2 wherein said iodine compound is selected from the group consisting of CHI3, Cl, C614 01' SH- I I l 3 

2. A method according to claim 1 which includes the steps of introducing said iodine compound into said envelope in solution in a volatile non-polar organic liquid, and thereafter removing said liquid from said envelope thereby to leave said solid iodine compound in said envelope.
 3. A method according to claim 1 wherein said iodine compound is selected from the group consisting of CHI3, CI4, GeI4 or SiI4.
 4. A method according to claim 2 wherein said iodine compound is selected from the group consisting of CHI3, CI4, GeI4 or SiI4. 